Suspension bent by stressed patch

ABSTRACT

The present invention provides a prebent ceramic suspension which includes a ceramic load beam which is bent by a stress patch. With thin film techniques the stress patch is formed on top of the load beam. In the preferred embodiment the patch is amorphous hydrogenated diamond-like carbon. When the suspension is on a wafer the carbon patch exerts a compressive stress on a top surface of the load beam just under the patch. When the suspension is released from the wafer the compressive patch exerts tensile forces on the top surface of the load beam causing an end of the load beam to bend toward the wafer. The amount of bending of the suspension can be accurately controlled by the cross sections of the load beam and the patch as well as the lateral dimensions of the patch. Further control can be achieved by controlling the hydrogen, nitrogen and other additive components of the carbon patch. After fabrication bending can be lessened by machining portions of the patch with a laser beam to effectively negate the stress of these portions. Still further, the patch can be laterally configured so that the suspension forms an arc when preloaded on a disk During fabrication various layers can be formed by thin film deposition to form an integrated magnetic head-slider-suspension. A pair of prebent ceramic suspensions can be preloaded on adjacent magnetic disks by a single actuator arm.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of application Ser. No.08/798,864 filed Feb. 11, 1997 U.S. Pat. No. 5,859,105 which is acontinuation application of application Ser. No. 08/474,616 filed Jun.7, 1995, U.S. Pat. 5,663,854.

CROSS-REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS

This application is related to:

(1) U.S. Pat. No. 4,167,765 by Watrous for "TRANSDUCER SUSPENSION MOUNTAPPARATUS";

(2) U.S. Pat. No. 4,670,804 by Kant et al. for "EXPANDABLE SUSPENSIONFOR A READ/WRITE HEAD IN A DISK FILE";

(3) U.S. Pat. No. 4,286,297 by Root et al. for "SUSPENSION FOR FLYINGMAGNETIC HEAD";

(4) U.S. Pat. No. 4,141,049 by Watrous for "LOADING MECHANISM FORNEGATIVE PRESSURE SLIDERS"; and

(5) Patent Application for "INTEGRATED SUSPENSION, ACTUATOR ARM AND COILASSEMBLY" by Fontana et al., Ser. No. 08.366,282.

The aforementioned patents and patent applications are commonly assignedto IBM and are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a prebent ceramic suspension and moreparticularly to an integrated suspension-slider-magnetic head for amultiple disk magnetic disk drive.

2. Description of the Related Art

A magnetic disk drive includes a magnetic disk and a magnetic head. Whenthe disk is rotated the magnetic head reads and writes magnetic signalson circular tracks on the disk. The magnetic head is typically mountedto a slider which is, in turn, mounted to a suspension (load beam), thesuspension biasing the slider toward the disk which is referred to inthe art as "preloading." The suspension is mounted to an actuator arm ofan actuator, the actuator being a voice coil or a longitudinal solenoiddepending upon whether the circular tracks of the disk are accessedradially or longitudinally. Both types of actuators employ anelectromagnet. If the actuator is a voice coil the actuator arm carriesa coil which, upon selective energization, cooperates with theelectromagnet to move the slider radially across the magnetic disk todesired tracks.

In a quiescent state of the disk drive the suspension preloads theslider on the magnetic disk. When the magnetic disk is rotated the diskswirls air between the disk and the slider producing a hydrodynamiclayer which separates the slider from the surface of the disk. When thisoccurs the slider and the magnetic head literally "fly" above or belowthe surface of the disk. The cushion of air is referred to as an "airbearing" and the surface of the slider riding on the air bearing isreferred to as an "air bearing surface" (ABS).

In a high capacity disk drive multiple double sided disks are verticallystacked and are I--read and written by multiple magnetic heads, themultiple magnetic heads being mounted to multiple sliders, the multiplesliders being mounted to multiple suspensions and the multiplesuspensions being mounted to multiple actuator arms. A pair ofsuspensions are mounted to a single actuator arm and the suspensions arepositioned between adjacent disks in the stack. With this arrangementone magnetic head reads and writes on the bottom of one disk and theother magnetic head reads and writes on the top of the other disk.

A typical prior art suspension is made from metal which is bent in aplastic state to bias the slider toward the disk. The slider, whichcarries the magnetic head, is bonded to one end of the suspension andthe other end of the suspension is affixed to one end of the actuatorarm. The attachment of the slider to the suspension and the attachmentof the suspension to the actuator arm is a labor intensified job. Thesliders are referred to as "chiplets" because they are small and arefabricated by thin film technology. Each chiplet has to be accuratelybonded to the suspension within a close tolerance. In order to simplifyfabrication of these disk drive components it has been proposed toconstruct are integrated magnetic head-slider-suspension by thin filmtechnology. The slider and the suspension are constructed of a ceramic,typically alumina. A copending patent application Ser. No. 08/166,282,filed Dec. 29, 1994, commonly assigned to IBM goes one step further andproposes constructing an integrated magnetichead-slider-suspension-actuator arm. The advantage of integrating thesecomponents is that they are connected with precision. With thin filmbatch construction literally hundreds of integrated units can be made ona single wafer.

In thin film construction multiple thin film layers are formed byphotopatterning, plating and sputtering on a wafer. When theconstruction is completed the integrated units are released from thewafer, each integrated unit being an integrated magnetichead-slider-suspension. All of these units are flat. The integratedmagnetic head-slider-suspension is then attached to an actuator arm. Inorder to bias the slider toward a disk one end of the suspension isattached to a slanted surface on the actuator arm. With this arrangementan actuator arm is employed with each suspension which results in twoactuator arms being employed between adjacent disks. This decreases diskstacking density as compared to the prior art single actuator arm whichcarries two prebent metallic suspensions. There is a strong felt need tocapitalize on the benefits of integrated magnetichead-slider-suspensions without losing disk stacking density in amultiple disk drive.

SUMMARY OF THE INVENTION

The present invention provides a prebent ceramic suspension whichincludes a stress patch on a ceramic load beam. A pair of prebentceramic suspensions can be connected to a single actuator arm in thesame manner that a pair of prior art prebent metallic suspensions areattached to a single actuator arm. Prebent ceramic suspensions canprovide the same disk stack density as the prior art prebent metallicsuspensions with the additional advantage that the magnetic head, theslider, the suspension and optionally the actuator arm can beintegrated. In the fabrication of the integrated unit various layers areformed on a wafer. These layers form the load beam and the slider, whichare typically alumina, and the magnetic head, which is a combination ofmagnetic layers and insulation layers. After completing these layers astress layer, which has a lateral patch configuration, is formed on topof the load beam near the actuator arm. The integrated unit is flatbefore it is released from the wafer and the patch stresses a topsurface of the load beam just under the patch. In the preferredembodiment the patch is amorphous hydrogenated diamond-like carbon.Before release of the integrated unit from the wafer the carbon patchexerts compressive stress on the top surface of the load beam just underthe patch. When the integrated unit is released from the wafer thecompressive patch causes the load beam, which carries the magnetic head,to bend toward the wafer. The amount of bending of the load beam can beaccurately controlled by the cross sections of the load beam and thepatch. The patch can be laterally configured so that the load beam formsan arc when loaded by the disk. Further control can be achieved bycontrolling the hydrogen, nitrogen and other additive components of thecarbon patch. Even after fabrication bending can be lessened bymachining portions of the patch with a laser beam to effectively negatethe stress of these portion.

An object of the present invention is to provide ceramic suspensionswhich can provide the same disk stack density as prior art metallicsuspensions but which have an additional advantage of integration with amagnetic head and slider by thin film deposition.

Another object is to provide a prebent ceramic suspension which enablestwo prebent suspensions to be loaded on adjacent magnetic disks by asingle actuator arm.

A further object is to provide an integrated magnetichead-slider-suspension and optionally integrated actuator arm with thesuspension prebent to provide desired preloading when contacting amagnetic disk.

Still another object is to provide an integrated prebent ceramicsuspension apparatus which has precisely placed magnetic head componentsand which precisely preloads a slider on a magnetic disk.

Still a further object is to provide a method of making the prebentceramic suspension apparatus of the present invention.

Other objects and attendant advantages of the present invention will bereadily apparent to one skilled in the art upon reading the followingdescription taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a plan view of a magnetic disk and a portion of a suspensionfor a magnetic disk drive.

FIG. 2 is a schematic illustration of the magnetic disk drive.

FIG. 3A is a side schematic illustration of a pair of ceramicsuspensions mounted to a pair of actuator arms prior to preloading onmagnetic disks.

FIG. 3B is the same as FIG. 3A except the ceramic suspensions have beenpreloaded on magnetic disks.

FIG. 4A is a side schematic illustration of the present prebent ceramicsuspensions mounted on a single actuator arm prior to preloading onmagnetic disks.

FIG. 4B is the same as FIG. 4A except the prebent ceramic suspensionshave been preloaded on magnetic disks.

FIG. 5 is a top plan illustration of the prebent ceramic suspensionintegrated with a magnetic head slider and leads.

FIG. 6 is a side illustration of the prebent suspension shown in FIG. 5.

FIGS. 7A and 7B illustrate two exemplary patches for pre-stressing aceramic load beam.

FIG. 8 is a plan view of an integrated magnetic head, slider, prebentsuspension and actuator arm of the present invention.

FIG. 9 is a side illustration of the prebent assembly shown in FIG. 8.

FIG. 10 is a side schematic illustration of the construction of theceramic load beam and compressive patch on the substrate.

FIG. 11 is a top plan illustration of FIG. 10.

FIG. 12 is a side illustration of the prebent suspension after releasefrom the substrate.

FIG. 13 is a block diagram of exemplary process steps for constructingthe prebent suspension.

FIGS. 14-16 illustrate another embodiment of the invention which omits arecess for receiving the patch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals designatelike or similar parts throughout the several views. There is shown inFIGS. 1 and 2 a magnetic disk drive 20 which includes a plurality ofvertically stacked double-sided magnetic disks 22. The disks aresupported on and rotated by a spindle 24, the spindle being rotated by adrive motor 26 which is controlled by a control unit 28. Each side ofeach disk has a plurality of concentric circular tracks which aremagnetically read and written by a plurality of magnetic heads, onemagnetic head being shown at 30 in FIG. 1, the magnetic heads beingresponsive to the control unit 28 via a read/write channel 32. Eachmagnetic head 30 is carried by a respective end portion (slider end) ofa prebent ceramic suspension 40 which is the subject of the presentinvention. Each ceramic prebent suspension 40 may be connected to anactuator arm 42 of an actuator with top and bottom actuator arms 42carrying a single prebent ceramic suspension 40 and the intermediatearms carrying a pair of prebent ceramic suspensions 40. Each actuatorarm 42 is fixed to a shaft 46 which is rotatably mounted in a basesupport 48 so that when the shaft 46 is rotated the magnetic heads atthe ends of the prebent suspensions 40 move in arcs to selected circulartracks on the magnetic disks 22. One of the actuator arms 42, such asthe bottom actuator arm may be provided with an extension which carriesa coil 50, the coil being adjacent to permanent magnets 52 so that whenthe coil 50 is selectively energized the magnetic heads are positionedover selected tracks on the magnetic disks 22. The magnetic head at theend portion of the top prebent ceramic suspension on each intermediateactuator arm engages the bottom surface of a disk 22 and the magnetichead at the end portion of the bottom prebent ceramic suspension on eachintermediate actuator arm engages the top surface of an adjacentmagnetic disk 22. When the disks 22 are rotated swirling air between thedisks and the suspensions cause each suspension to ride on a cushion ofair (air bearing) with a slight spacing between the surface of the diskand the suspension, such as 0.075 microns. In some embodiments it may bedesirable for the slider end of the suspension to contact the surface ofthe disk with minimal pressure. The prebent ceramic suspensions of thepresent invention provide increased disk stacking density over prior artflat ceramic suspensions and further enable integration of the magnetichead, slider, suspension and optionally the actuator arm which is notachievable by prior art metallic suspensions. These advantages will bedescribed in more detail hereinafter.

FIG. 3A is a side view of a pair of prior art flat ceramic suspensions54 which are connected to a pair of prior art actuator arms 55. Theprior art ceramic suspensions 54 are constructed by thin film technologywhich is necessary in order to integrate the magnetic head componentsand leads with the suspension. After release from a wafer each ceramicsuspension 54 is flat as shown in FIG. 3A. In order to obtain preloadingof the slider ends 56 of the ceramic suspensions against surfaces ofadjacent disks each suspension must be angled toward a respective diskas shown in FIG. 3A. This is achieved by attaching an end portion 57 ofeach suspension to an angled surface 58 on each actuator arm 55. FIG. 3Bshows the prior art ceramic suspensions 54 preloaded on a pair ofmagnetic disks 22.

FIG. 4A shows a side view of a pair of the present prebent ceramicsuspensions 40. Since the prebent ceramic suspensions 40 are alreadybent they can be mounted on a single actuator arm 42. FIG. 4B shows theprebent ceramic suspensions 40 preloaded on top and bottom adjacentmagnetic disks 22. With the present intention, disk stacking density isincreased over disk stacking density of prior art ceramic suspensions54. This is because one actuator arm 42 carries two prebent suspensions40 whereas in the prior art each actuator arm 55 carries only one priorart suspension 54. There is another reason for increased disk stackingdensity which will be explained in detail hereinafter. Further, magneticdisk drives, which employ prebent suspensions, use less actuator armswhich reduces weight and cost.

FIG. 5 shows an exemplary prebent integrated ceramic suspension 60 whichintegrates a load beam 61 with a slider at 62, a magnetic head 64 andleads 66 and 68 which interconnect components of the magnetic head topads 70. As will be explained in more detail hereinafter, a patch 80 ofcompressive material is employed for bending the suspension. Thepreferred lateral shape of the patch is trapezoidal which provides anadvantage which will be described in more detail hereinafter. It ispreferred that the patch and consequently the bending be located closerto the end of the load beam opposite the magnetic head 64 so as toincrease the moment arm upon preloading. The trapezoidal patch is shownalso in FIG. 7A and a rectangular patch 82 is shown in FIG. 7B. Thecompressive patch 80 exerts a compressive force on the top surface ofthe ceramic suspension which causes the ceramic suspension to bend toprovide the desired preloading. The patches in FIGS. 7A and 7B wereemployed in various embodiments to illustrate the bending of the ceramicsuspension. FIG. 6 shows a side view of the ceramic suspension of FIG. 5being bent by the patch 80 to provide a desired preloading. The slider62 is a bottom end portion of the suspension. The slider 62 is supportedby the air bearing against the bending force of the suspension uponrotation of the magnetic disk.

In the preferred embodiment the beam 61 has a reduced cross-sectionacross its width which provides a recess 69 for receiving the patch 80.When the suspension is preloaded on a disk practically all of thebending will take place at the reduced cross-section. This causes theremainder of the suspension toward the magnetic head to assume a flatterconfiguration upon preloading on a disk. The flatter configuration takesup less vertical space and is a second factor which increases diskstacking density.

In FIGS. 8 and 9 there is shown an integrated magnetichead-slider-suspension-actuator arm 90. In this embodiment an actuatorarm portion 92 may include the pads 70, an opening 94 for receiving theshaft 46, shown in FIG. 2, and the coil 50 which is also shown in FIG.2. The compressive patch 80 is shown in the recess 69 of the suspensionportion adjacent the actuator arm portion 92. A side view of the prebentintegrated assembly is shown in FIG. 9. In an actual embodiment of theintegrated assembly 90 the actuator arm portion 42 would be about twiceas wide and would be supported by a metal plate.

FIGS. 10-13 describe the method of making the prebent ceramic suspension60 or 90 at 100. FIG. 10 shows a load beam 101 formed on a substrate102. The substrate 102 may be a wafer which supports the construction ofliterally hundreds of ceramic suspensions. The load beam is made of anysuitable ceramic material such as alumina (AL₂,O₃). A patch 104 ofstressed material applies a force on the top surface of the load beamimmediately below the patch. This patch can be made of compressivematerial. The preferred material is amorphous hydrogenated diamond-likecarbon (DLC). Other suitable materials are amorphous carbon or amorphousdiamond. A top view of a single ceramic load beam and compressive patchon the substrate is illustrated in FIG. 11. When the suspension 100 isreleased from the substrate, the compressive patch 104 expands to applytensile forces to the top surface of the ceramic load beam immediatelybelow the patch. This causes the ceramic load beam to bend as shown inFIG. 12. It should be understood that the suspension 100 is intended torepresent an integrated magnetic head-slider-suspension 60 as shown inFIG. 5 or an integrated magnetic head-slider-suspension actuator arm 90as shown in FIG. 8.

A detailed method of making the integrated suspension is shown in blockdiagram in FIG. 13. Thin film techniques are employed which includeelectroplating, sputtering, plasma-assisted chemical vapor deposition(PACVD) and photopatterning with photoresist. As shown in FIG. 13, thefirst step is to deposit a release layer on the substrate. The releaselayer, which may be copper, is employed for releasing the ceramicsuspensions later in the construction. The next step is to deposit aceramic layer on the release layer. The ceramic layer is non-ductile andis preferably alumina. The ceramic layer, which may be about 10 μmthick, is then provided with a hole by photopatterning arid etching.This hole will cause the recess 69 (See FIGS. 6 and 9) when a subsequentceramic layer is deposited. During formation of the ceramic layer orlayers, the magnetic head, leads, pads, and optionally, an actuator armwith an actuator coil may be fabricated. With these steps, the stage isset for an integrated magnetic head-slider-suspension 60 as shown inFIG. 5 or an integrated magnetic head-slider-suspension-actuator arm 90as shown in FIG. 8. A final or additional ceramic layer, which may be 20μm thick, is deposited which fills the hole of the first ceramic layerand provides the recess 69. The ceramic layers may be formed bysputtering and the components for the magnetic head, leads, pads andactuator coil may be formed by plating and sputtering along withphotopatterning.

The next step is to deposit a stress layer on the ceramic layer. Thestress layer is preferably a compression layer of amorphous,hydrogenated, diamond-like carbon. This may be accomplished by a varietyof beam-assisted methods, such as plasma-assisted chemical vapordeposition (PACVD), sputtering, ion beam, cathodic arc, or laserdeposition techniques. The preferred techniques are radio frequencyplasma-assisted chemical vapor deposition (RF PACVD) or direct currentplasma-assisted chemical vapor deposition (DC PACVD). PACVD is conductedin a chamber which has parallel plate electrodes, one of the electrodesbeing positive and the other electrode being negative. The substrate isconnected to the negative electrode and radio frequency or DC current ispassed therebetween. DC current is employed when the ceramic layer is ona conductive layer such as the copper release layer. RF current isemployed when the current must penetrate insulation layers to thenegative electrode. A precursor, which contains carbon and hydrogen suchas acetylene, methane, and cyclohexane, is employed in the chamber. Byusing the various deposition techniques, precursors, temperatures andpressures various compressive stresses can be developed within theamorphous hydrogenated diamond-like carbon layer. Tests which were runto show the various compressive stresses are set forth in the followingfour examples:

EXAMPLE 1 Deposition by RF PACVD

Precursor=acetylene

Pressure=30 mtorr

RF power density=150 mW.cm⁻²

Substrate temperature=180° C.

Substrate bias=-150 V DC (substrate positioned on powered electrode)

Obtained stress=1.6 GPa, compressive

EXAMPLE 2 Deposition by RF PACVD

Precursor=acetylene

Pressure=30 mtorr

RF power density=100 mW.cm⁻²

Substrate temperature=180° C.

Substrate bias=-80 V DC (substrate positioned on powered electrode)

Obtained stress=1.25 GPa, compressive

EXAMPLE 3 Deposition by DC PACVD

Precursor=methane

Pressure=100 mtorr

DC bias=-800 V

Substrate temperature=180° C.

Substrate bias=-800 V DC

Obtained stress=1.4 GPa, compressive

EXAMPLE 4 Deposition by DC PACVD

Precursor=cyclohexane

Pressure=100 mtorr

DC bias=-800 V

Substrate temperature=180° C.

Substrate bias=-800 V DC

Obtained stress=0.65 GPa. compressive

When current is passed between the electrodes the precursor gas ionizesand charged carbon ions attack the negative electrode which results indeposition of the amorphous hydrogenated diamond-like carbon on thesubstrate target. The above stresses can further be controlled by dopingthe precursor with hydrogen, nitrogen, fluorine, silicon or acombination thereof. The precursor is a hydrocarbon so that doping withhydrogen will generally increase the stress while doping with nitrogenwill generally decrease the stress.

The construction and stress results of forming diamond-like carbon filmsby RF PACVD and DC PACVD are explained in the following publishedarticles:

1. "Diamondlike carbon films by rf plasma-assisted chemical vapordeposition from acetylene" in IBM Journal of Research and Development,Vol. 34, No. 6, November 1990, by Grill, Meyerson and Patel;

2. "The Effect of Deposition Conditions or the Optical and TribologicalProperties of Annealed Diamond-Like Carbons Films" in R. E. Clausing, L.L. Horton, J. C. Angus and P. Koidl (eds.), Diamond and Diamond-LikeFilms and Coatings, NATO-ASI Series B; Physics. Plenum, New York, 1991,Vol. 266, p. 417 by Grill, Patel and Meyerson;

3. "Diamondlike Carbon Deposited by DC PACVD" in Diamond Films andTechnology, Vol 1, No. 4, 1992, by Grill and Patel;

4. "Nitrogen-Containing Diamondlike Carbon Prepared by DC PACVD" inDiamond Films and Technology, Vol 2, Nos. 2 and 3, 1992, by Grill andPatel; and

5. "Stresses in diamond-like carbon films" in Diamond and RelatedMaterials, 2 (1993), by Grill and Patel.

The next step is to photopattern the stress layer to define a patch areaof the stress layer. This is an important step since the photopatterningestablishes the stress which will be applied to the ceramic load beamimmediately below the patch. Examples of two shapes of the patches areshown in FIGS. 7A and 7B. The preferred shape of the patch istrapezoidal as shown in FIG. 7A. The trapezoidal patch is bounded byshort and long parallel edges and a pair of tapered edges. The patch inFIG. 7A progressively increases in cross-section from its short edge toits long edge. With the trapezoidal patch, the stress applied to theceramic layer immediately under the patch progressively increases fromthe short edge of the patch to the long edge of the patch. Otherwise,the compressive stress along the longitudinal axis of the suspensionbeneath the trapezoidal patch is not constant whereas the compressivestress due to the rectangular patch shown in FIG. 7B is constant. Byproperly designing the lateral area and thickness of the trapezoidalpatch, shown in FIG. 7A, the stress on the ceramic load beam immediatelybeneath the patch can be made to be constant upon preloading thesuspension on a disk because of the varying moment arm of thesuspension. With this arrangement the load beam below the trapezoidalpatch is an arc of a circle. This greatly facilitates the design of thesuspension for a desired preloading.

The next step is to remove the stress layer in the field about thepatch. This may be accomplished by etching, such as reactive ion etching(RIE). The next step is to strip the photoresist which covers the patch.The next step is to deposit a metallic film, such as chromium, over theentire wafer. The thickness of the chromium film may be in the order of1,000 to 2,000 Å. The next step is to photopattern the metallic film todefine an integrated suspension. The next step is to remove the metallicfilm in the field about the integrated suspension. This leavesphotoresist on top of the metallic film which is on top of the desiredconfiguration for the integrated suspension. The next step is to removethe ceramic layer in the field about the integrated suspension down tothe release layer which forms an integrated suspension which is attachedto the release layer. The next step is to strip the photoresist layer ontop of the integrated suspension. The next step is to simultaneouslyrelease the integrated suspension from the substrate and strip themetallic film. This may be accomplished with a dissolvant which attacksboth the release film and the metallic film. This step provides thecompleted integrated suspension. When multiple suspensions are beingformed on a wafer the photopatterning is employed to pattern each of thesuspensions. The suspension can then be affixed by bonding to anactuator arm or if the integrated suspension is integrated with theactuator arm, the actuator arm is mounted in the actuator assembly.

It should be understood that preloading a ceramic suspension on a diskmust be precise. Accordingly, the angled ends 58 of the actuator arms55, shown in FIGS. 3A and 3B, must be within a tolerance of a fewmicroradians. Since these angled surfaces are machined, this is adifficult tolerance to maintain. The result is unreliable preloading bythis type of ceramic suspension. This is not a problem with the prebentsuspension since the pre-bending can be accurately controlled by thinfilm construction. The prebent ceramic suspension, which has a reducedcross-section at the location of the patch, has an added advantage inthat the magnetic head or slider end of the ceramic suspension getsflatter quicker with respect to the magnetic disk than the prior artceramic suspension. Accordingly, the stacking density of disk drivesemploying the prebent suspensions is greater than disk drives whichemploy the prior art ceramic suspensions. Another advantage of theprebent suspension is that it can be altered after construction byannealing or trimming the patch above 400° C. with heat such as a laserbeam or an infrared beam. For instance, if the stress is too great onthe ceramic beam, portions of the patch can be hit with a laser beamwhich will effectively nullify the stress of the hit portions.

Another ceramic suspension 110 is shown in FIGS. 14-16 wherein the loadbeam 112 does not have s recess for the patch 80. Calculations were madefor this suspension without the integrated components. The ceramicsuspension was 12 mm long with a 0.9 mm width and 1 mm long with a 1 mmwidth, these widths being shown in FIG. 5. The thickness of thesuspension was 26 μm. The trapezoidal patch 80 was 1-1/2 mm long, theshort edge was 0.24 mm long, the long edge was 0.3 mm long and thethickness was 0.7 mm. The material of the suspension was alumina and thematerial of the patch was amorphous hydrogenated diamond-like carbon.

Calculations for the prebent ceramic suspension are set forthhereinbelow. The calculations first compute the residual stress in thealumina/DLC sandwich before it is released from the substrate. Oncereleased from the substrate, the stress will redistribute, as will thestrain. From a calculation of the new stress distribution, one candetermine how much of the strain is extensional, and how much goes intobending. This bending strain then can be used to compute the deflectionangles and deflected position of the beam. Throughout the calculations,one dimensional beam theory is used. For accuracy the deformation of thealumina/DLC system in the width direction should be small; otherwise,anticlastic curvature could result (i.e. the beam would bend like a tapemeasure), and the beam tip will deflect much less. Therefore, the widthof the patch should be kept to less than half the width of the beam. Thestress distribution through the thickness of the beam is given by:

    σ(z)=σ.sub.r (z)+E(z)·ε(z)

where the first term on the right hand side is a residual stress, andthe second is the deformation produced by the overall stress state. Forconvenience it is assumed that the stress out of the plane of thecenterline of the beam is not important. The strain is assumed to be ofthe form

    ε(z)=ε.sub.0 +ε.sub.1 ·z

where the terms on the right hand side are respectively the constantlongitudinal extension of the beam and a linearly varying strain term.The sought after term is the linearly varying strain term since it willprovide the beam curvature, which will in turn provide how much momentis required to straighten out the beam. Substitution of the secondequation into the first gives:

    σ(z)=σ.sub.r (z)=E(z)·(ε.sub.0 +ε.sub.1 ·Z)

To compute the forces and moments on the beam the above expression isintegrated. The longitudinal force is given by

    T.sub.x =∫.sub.A σ(z)dA

while the moment is given by

    M.sub.y =∫.sub.A z·σ(z)dA

The force and moment conditions on the beam after the Alumina/DLCstructure has been released from the substrate are

    T.sub.x =0 and M.sub.y =0

The residual stresses are

    σ.sub.r =σ.sub.DLC in diamond like carbon coating

    σ.sub.r 0 in alumina layer

The alumina and DLC will be assumed to have rectangular cross sections;they do not however need to have the same widths. In fact, it willprobably be beneficial in reducing the lateral warpage if the DLC isless than half the width of the beam. The alumina is taken to extendfrom h₁ to h₂, with width W_(A), while the DLC extends from h₂ to h₃with a width W_(DLC). In general, both the thicknesses h and the widthsof both the alumina and the DLC are functions of the position along thelength of the beam. Integration of the force condition gives theconstant strain term in terms of the linear term as

    ε.sub.0 α·ε.sub.1 +β

where ##EQU1## Integration of the moment condition produces the relation

    ψ·ε.sub.1 +γ·ε.sub.0 δ=0

where ##EQU2## When these expressions are combined with the oneresulting from the force condition, solving for the linear strain termgives: ##EQU3## This term is the curvature of the beam. From beamtheory, the slope of a point along the beam length is ##EQU4## where thecurvature is permitted to be a function of position along the beam. Thiswould be the case if any of the material properties or dimensions ofeither the ceramic or the compressive layer were to vary along the beamlength. The deflection along the beam is found through ##EQU5## The tipdeflection is given by ##EQU6## In the ensuing analysis the compressivepatch has a trapezoidal shape and the beam is rectangular and that thecross sections of both are rectangular. Then, the shape of thecompressive patch is given by ##EQU7## where the DLC patch starts at x=0and extends to LDLC, with widths W_(DLC1) and W_(DLC2), respectively.The following values are assumed to calculate angle of beam tip θ(L) andbeam tip deflection u(L) in conjunction with the following formulas:##EQU8## The final suspension shape is given by the sum of the shape dueto the tip loading and the initial curved shape produced by thepre-bending patch. Since the strain is small and the deformation anglesare moderate it is assumed that linear superposition holds.

The deformation of a cantilever beam with a concentrated load at its tipis given by: ##EQU9## which is referenced in Roark, R., and Young, W.,Formulas for Stress and Strain, 5th edition. p. 96. From the first ofthe above expressions, the load required to deflect the suspensionthrough a given angle is ##EQU10## In the ensuing calculations theeffect of the prebend patch on the stiffness of the suspension isignored since for a thin patch the change in stiffness will be less thana few percent. A suspension is desired in which both the base and thehead are at the same angle. With the following values and formulas theload W which neutralizes the end rotation produced by the prebending canbe determined. ##EQU11## The load required is ##EQU12## The differencein position between top surfaces at the base and the tip of thesuspension is found by subtracting the deflection caused by this loadingfrom the deflection produced by the prebending of the part. This isgiven by ##EQU13## It is obvious from the above calculations that thestress applied by the patch to the ceramic suspension can be accuratelycontrolled to provide a precise preloading.

Obviously, other embodiments and modifications of the invention willoccur to those of ordinary skill in the art in view of the aboveteachings. Therefore, the invention is to be limited only by thefollowing claims which include all such embodiments and modificationswhen view in conjunction with the above specification and accompanyingdrawings.

We claim:
 1. A prebent ceramic suspension for a magnetic disk drivecomprising:an elongated ceramic load beam which has first and secondsurfaces which are bounded by first and second ends and first and secondsides, the beam having a longitudinal axis which extends between thefirst and second ends; a patch of stressed material on the first surfaceof the beam which stresses the first surface and causes the beam tobend.
 2. A magnetic disk drive including a pair of suspensions asclaimed in claim 1 including:an actuator which has an actuator arm; saidpair of suspensions being mounted at first ends to the actuator arm; amagnetic disk mounted on a rotatable spindle; and second ends of saidpair of suspensions being preloaded on surfaces of adjacent magneticdisks.
 3. A combined suspension and actuator arm which includes firstand second suspensions as claimed in claim 1 comprising:each suspensionhaving first and second end portions; an actuator arm having top andbottom surfaces; the first end portions of the first and secondsuspensions being connected to the top and bottom surfaces respectivelyof the actuator arm with the second end portions of the first and secondsuspensions extending therefrom.
 4. A suspension as claimed in claim 1wherein the load beam has a recess which receives the patch.
 5. Asuspension as claimed in claim 1 wherein the bend in the load beamprovides preloading of the load beam on a magnetic disk.
 6. A suspensionas claimed in claim 1 wherein the load beam is alumina.
 7. A suspensionas claimed in claim 1 including:the patch being located at a first endportion of the load beam; and a magnetic head located at a second endportion of the load beam.